Question 973151
Let the measures of the angles be x, x, y and z.


According to the description and assigned variables,
{{{system(y=2x,z=-60+2(2x+y),2x+y+z=360)}}}.
Forming that system is the first objective in the solution process.  Solving the system for x, y, and z is the second objective of the solution and will reach the finish.